1. Field of the Invention
The present invention relates to an LED lighting control means, and more particularly, to an LED lighting control integrated circuit having embedded programmable nonvolatile memory.
2. Description of the Prior Art
Due to lightweight, small size, low power consumption and high-bright lighting capability, light emitting diodes (LEDs) are now in widespread use, including a variety of indication applications, indoor or outdoor lighting applications, vehicle auxiliary lighting applications, camera flashlights, backlights for different display panels, and so forth. In advanced applications, LED lighting modules are required to generate light outputs having high-precision luminance and chromaticity. However, the luminance and chromaticity of the light emitted from the LED lighting modules are changed in response to temperature variation, aging degradation, and power-on time, etc. Accordingly, a variety of LED lighting control means are set forth to provide an accurate lighting control for the LED lighting modules so as to generate light outputs having desired luminance and chromaticity.
Please refer to FIG. 1, which is a functional block diagram schematically showing a prior-art LED lighting control device 101. The LED lighting control device 101 is utilized to control an LED lighting module 190. The LED lighting module 190 comprises a red LED unit 191, a green LED unit 192, and a blue LED unit 193. For backlight applications in display panels, a light guide plate and a diffuser are installed for distributing the light emitted from the LED lighting module 190. In general, a photo sensor 197 is attached to the LED lighting module 190 for detecting the intensity of light emitted from the LED lighting module 190 for generating an analog luminance signal. Besides, a temperature sensor 198 is also attached to the LED lighting module 190 for detecting the temperature of the LED lighting module 190 for generating an analog temperature signal.
The LED lighting control device 101 comprises a lookup table (LUT) unit 110, a timer 120, a signal processing unit 130, a pulse-width-modulation (PWM) signal generator 140, a driving circuit 150, and two analog-to-digital converters (ADCs) 187 and 188. The analog-to-digital converter 188 converts the analog temperature signal received from the temperature sensor 198 into a digital temperature signal. The analog-to-digital converter 187 converts the analog luminance signal received from the photo sensor 197 into a digital luminance signal. The timer 120 is utilized to count an accumulated operating time of the LED lighting module 190 for generating a first timing signal. The timer 120 may also function to count an elapsed operating time of the LED lighting module 190 each time after power-on for generating a second timing signal.
The lookup table unit 110 comprises an electrical-erasable programmable read-only-memory (EEPROM) for storing a plurality of lookup tables. The plurality of lookup tables provide information for controlling light outputs of the LED lighting module 190. The information provided by the lookup table unit 110 may comprise compensation data for the red, green, and blue LED units 191-193 concerning temperature variation, aging degradation, and power-on time, etc. That is, the lookup table unit 110 functions to provide compensation data based on the first timing signal, the second timing signal, the digital temperature signal, and the digital luminance signal. The signal processing unit 130 generates control signals Cr, Cg, and Cb based on the compensation data provided by the lookup table unit 110. The PWM signal generator 140 regulates the duty cycles of PWM signals Sr, Sg, and Sb based on the control signals Cr, Cg, and Cb respectively. The driving circuit 150 adjusts the driving currents Ir, Ig, and Ib according to the PWM signals Sr, Sg, and Sb respectively so that the LED lighting module 190 is able to generate light outputs having desired luminance and chromaticity. However, manufacture of the electrical-erasable programmable read-only-memory requires complicated integrated circuit (IC) fabrication processes, and the compensation functionalities of the LED lighting control device 101 cannot meet future demands for advanced performances.
Since the LED lighting control means is required in a variety of LED lighting applications, different compact designs having more compensation or calibration functionalities have been extensively developed uninterruptedly.